In "Thanks for All the Fish", Fenchurch finds the Hitchhiker's Guide which Arthur left in her brother's car when Arthur was...well...hichhiking. She reads about the places in the book and asks Arthur about them when he randomly shows up at her house. The book even points out the "DONT PANIC" text at that point. Neither character, during this conversation, has a Babel fish install in their ears yet both are apparently able to read the alien work.
Why was Fenchurch, specifically, able to read the Guide?
(Note: this is clearly not a duplicate of my Babel fish question as neither character has a Babel fish as stated above.)